The present invention relates to a dielectric ceramic composition for microwave use having a relative permittivity xcex5r of 35 to 45, Qf0 value of at least 50,000 GHz (at 7 GHz) and a dielectric characteristic of xcfx84f=0xc2x110 ppm/xc2x0 C. employed for microwave communication filters, milliwave communication filters, oscillators, inductor antennas, and frequency adjusting rods etc.
Dielectric ceramic compositions are widely employed in the high-frequency region such as microwaves and milliwaves in for example dielectric resonators, dielectric substrates for MIC and waveguides. The characteristics that these are required to have are: (1) a large relative permittivity xcex5r to meet demands for miniaturization, since the wavelength is reduced to 1/xcex5r1/2 in a dielectric, (2) low dielectric loss at high frequency i.e. high Q value, and (3) small and stable temperature coefficient xcfx84f of resonance frequency.
Conventional examples of such a dielectric ceramic composition are Laxe2x80x94Tixe2x80x94Alxe2x80x94O based compositions (see Japan, J. Appl. Phys. 36 (1997) 6814), which have xcex5r=36, Qf0 value=45,000 GHz, and xcfx84f=xe2x88x922 ppm/xc2x0 C., but their Qf0 values are low.
Also, in the case of Ba(Zn1/3Nb2/3)O3 based compositions (published in: Electronics/Ceramics September 1993 September page 3), xcex5r=41, Qf0 value=86,000 GHz, and xcfx84f=+31 ppm/xc2x0 C., but a dielectric ceramic composition of small xcfx84f is not obtained.
Recently, La2O3.Al2O3.SrO.TiO2 based composition or La2O3.Al2O3.SrO.TiO2.CaO based composition or composition containing one or two or more of Ce, Nb, Ta, Y, Zr, V, Cr, Mo, W, Co, Ni, Cu, Zn, Sn, Bi, B, or Si in the aforementioned ceramic compositions (see Laid-open Japanese Patent Publication H. 11-130528) has been proposed.
Regarding the dielectric characteristic of these ceramic compositions, they have excellent dielectric characteristics with xcex5r of more than 30, Qf0 value more than 25,000 GHz (at 1 GHz) and xcfx84f less than +30 (ppm/xc2x0 C.), but dielectric ceramic compositions of low xcfx84f are not obtained. Recently, with increasingly severe demands for miniaturization of portable terminal electronic equipment, materials of even better dielectric performance are being demanded.
In view of the foregoing demands, an object of the present invention is to provide a dielectric ceramic composition for microwave use having a relative permittivity xcex5r of 35 to 45, Qf0 value of at least 50,000 GHz (at 7 GHz) and a dielectric characteristic of xcfx84f=0xc2x110 ppm/xc2x0 C.
The present invention studied various compositions with the object of obtaining a material capable of being controlled to a relative permittivity xcex5r of 35 to 45, Qf0 value of at least 50,000 GHz (at 7 GHz) and a dielectric characteristic of xcfx84f=0xc2x110 ppm/xc2x0 C, and, as a result, discovered that, with an La2O3.Al2O3.SrO.TiO2 based ceramic composition, by adding a specific quantity of Ga2O3 to the aforesaid ceramic composition, the Qf0 value could be increased, and, by further adding a specific quantity of Pr2O3, control of the xcfx84f value became possible, so that a ceramic composition capable of being controlled to a relative permittivity xcex5r of 35 to 45, Qf0 value of at least 50,000 GHz (at 7 GHz) and a dielectric characteristic of xcfx84f=0xc2x110 ppm/xc2x0 C could be obtained, and thereby perfected the present invention.
Specifically, the present invention consists in a dielectric ceramic composition for microwave use characterized in that the compositional formula is expressed by aAl2O3.bGa2O3.cTiO2.dSrO.eLa2O3.fPr2O3, where a, b, c, d, e and f representing the mol ratios satisfy the following values (the case where b and f are simultaneously 0 is excluded).
a+b+c+d+e+f=1
0.079xe2x89xa6axe2x89xa60.167
0xe2x89xa6bxe2x89xa60.017
0.333xe2x89xa6cxe2x89xa60.412
0.333xe2x89xa6dxe2x89xa60.412
0.035xe2x89xa6exe2x89xa60.167
0xe2x89xa6fxe2x89xa60.101
The reasons why, in the present invention, if the respective mol ratios of Al2O3, Ga2O3, TiO2, SrO, La2O3 and Pr2O3 are a, b, c, d, e, f, these mol ratios are respectively restricted to 0.079xe2x89xa6axe2x89xa60.167, 0xe2x89xa6bxe2x89xa60.017, 0.333xe2x89xa6cxe2x89xa60.412, 0.333xe2x89xa6dxe2x89xa60.412, 0.035xe2x89xa6exe2x89xa60.167, and 0xe2x89xa6fxe2x89xa60.101 are as follows.
If a is less than 0.079, xcex5r increases but the Qf0 value is less than 50,000 GHz, but if it exceeds 0.167 mol ratio, xcex5r is lowered and drops to 35 or lower, which is undesirable.
If b exceeds 0.017 mol ratio, the Qf0 value is lowered, resulting in the Qf0 value dropping below 50,000 GHz, which is undesirable.
If c is less than 0.333 mol ratio, or is lowered, falling to 35 or lower, which is undesirable; if it exceeds 0.412 mol ratio, xcex5r increases, but the Qf0 value drops below 50,000 GHz, which is undesirable.
If d is less than 0.333 mol ratio, xcex5r is lowered, falling to 35 or lower, which is undesirable; if it exceeds 0.412 mol ratio, xcex5r increases, but the Qf0 value drops below 50,000 GHz, which is undesirable.
If e is less than 0.035 mol ratio, xcex5r is increased, but the Qf0 value drops below 50,000 GHz, which is undesirable; if it exceeds 0.167 mol ratio, xcex5r is lowered, falling to 35 or lower, which is undesirable.
If f exceeds 0.101 mol ratio, If becomes quite large, becoming 10 ppm/xc2x0 C. or more, which is undesirable.